The present disclosure relates to an intermediate transfer belt that temporarily holds a toner image which is formed on an image carrier and transferred to the intermediate transfer belt, and a tandem color image forming apparatus provided with the same intermediate transfer belt.
Conventionally, color image forming apparatuses such as a color printer, color facsimile and the like have widely adopted a method, hereinafter referred to as “tandem method”. The tandem method includes a primary transfer and a secondary transfer that is performed subsequent to the primary transfer. In the primary transfer, a toner image of each color (e.g., each of four colors, magenta, cyan, yellow, black) is primarily transferred from a plurality of image carriers (e.g. photoreceptor drums) arranged in tandem to an intermediate transfer belt. In the secondary transfer, the toner image on the intermediate transfer belt is secondarily transferred to a sheet of paper through a secondary transfer roller.
As one of problems which occur in a tandem color image forming apparatus using the intermediate transfer belt, a white spot image or a disordered image may be named, both of which are generated due to discharging performed during a secondary transfer. The disordered image is caused by the incomplete transfer of toner from the intermediate transfer belt to a surface of the sheet of paper due to a gap between them. To cope with such a problem, it is generally practiced that a coat layer (electrically high resistance layer) is formed on a surface of the secondary transfer roller to prevent the generation of discharging. In addition, an image forming apparatus has been known, which is provided with charging means for controlling an amount of electrostatic charge on toner existing on the intermediate transfer belt.
However, provision of the coat layer on the secondary transfer roller may lead to a new problem such as an increase in cost and a decrease in paper carrying performance and durability. Provision of any charging means may correspondingly increase the number of required components, thereby causing an increase in cost such as the case in which the coat layer is provided.